To enlarge a particular photo, left-click once on it.
Note: When a picture becomes enlarged, if you hold
your Mouse Pointer over it, the Mouse Pointer will
turn into a tiny circle with a Plus sign in it. At that
shape, if you left-click once, the picture will become
even larger than it was. Then the Pointer turns into
a small Minus sign, and if you left-click once, the
picture will be reduced back to its original size.